1. Field of the Invention
The present invention relates to vacuum circuit breakers. More particularly, the present invention relates to circuit breakers having a high speed mechanically interlocked impedance grounding switch. The present invention also relates to circuit breakers and impedance grounding switches for use in collection feeders of wind and solar farms as well as distribution feeders of distributed generation systems.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Medium voltage collection feeders in wind and solar applications are usually subject to ground fault overvoltage when feeder circuit breakers open during a feeder ground fault. This also occurs in 4-wire multigrounded neutral feeders having ungrounded or ineffectively grounded distributed generation sources feeding in.
An impedance grounding switch is a device intended to close and connect a load bank impedance in parallel connection with the feeder. This closing and connecting can occur an instant before the feeder circuit breaker opens as consequence of a feeder ground fault. As such, the impedance grounding switch provides the ability to suppress such ground fault overvoltages.
The interruption of electrical power circuits has always been an effect of either a circuit breaker or switch. This interruption can occur as a protective measure or a power management decision. In early switching techniques, circuits could be broken only by separation of contacts in air followed by drawing the resulting electric arc out to such a length that it could no longer be maintained. The basic problem is to control and quench the high power arc. This necessarily occurs at the separating contacts of a switch or breaker when opening high current circuits. Since arcs generate a great deal of heat energy which is often destructive to the contacts, it is necessary to limit the duration of the arc and to develop contacts that can withstand the effect of the arc during multiple occurrences.
A vacuum switch or circuit breaker uses the rapid dielectric recovery and high-dielectric strength of the vacuum. A pair of contacts are hermetically sealed in a vacuum envelope. An actuating motion is transmitted through bellows to the movable contact. When the electrodes are parted, an arc is produced and supported by metallic vapor boiled from the electrodes. Vapor particles expand into the vacuum and condense on solid surfaces. At a natural current zero, the vapor particles disappear and the arc is extinguished.
In the past, various patents have issued relating to such vacuum switches and circuit breakers. For example, U.S. Pat. No. 5,612,523, issued on Mar. 18, 1997 to Hakamata et al., teaches a vacuum circuit-breaker and electrode assembly. A portion of a highly conductive metal member is infiltrated in voids of a porous high melting point metal member. Both of the metal members are integrally joined to each other. An arc electrode portion is formed of a high melting point area in which the highly conductive metal is infiltrated in voids of the high melting point metal member. A coil electrode portion is formed by hollowing out the interior of a highly conductive metal area composed only of the highly conductive metal and by forming slits thereon. A rod is brazed on the rear surface of the coil electrode portion.
U.S. Pat. No. 6,048,216, issued on Apr. 11, 2000 to Komuro, describes a vacuum circuit breaker having a fixed electrode and a movable electrode. An arc electrode support member serves to support the arc electrode. A coil electrode is contiguous to the arc electrode support member. This vacuum circuit breaker is a highly reliable electrode of high strength which undergoes little change with the lapse of time.
U.S. Pat. No. 6,759,617, issued on Jul. 6, 2004 to S. J. Yoon, describes a vacuum circuit breaker having a plurality of switching mechanisms with movable contacts and stationary contacts for connecting/breaking an electrical circuit between an electric source and an electric load. The actuator unit includes at least one rotary shaft for providing the movable contacts with dynamic power so as to move to positions contacting the stationary contacts or positions separating from the stationary contacts. A supporting frame fixes and supports the switching mechanism units and the actuator unit. A transfer link unit is used to transfer the rotating movement of the rotary shaft to a plurality of vertical movements.
U.S. Pat. No. 7,223,923, issued on May 28, 2007 to Kobayashi et al., provides a vacuum switchgear. This vacuum switchgear includes an electro-conductive outer vacuum container and a plurality of inner containers disposed in the outer vacuum container. The inner containers and the outer container are electrically isolated from each other. One of the inner vacuum containers accommodates a ground switch for keeping the circuit open while the switchgear is opened. A movable electrode is connected to an operating mechanism and a fixed electrode connected to a fixed electrode rod. Another inner vacuum container accommodates a function switch capable of having at least one of the functions of a circuit breaker, a disconnector and a load switch.
It is an object of the present invention to provide a vacuum circuit breaker system including an integral high-speed impedance grounding switch at a relatively low cost.
It is a another object of the present invention to provide a vacuum circuit breaker system including an integral high-speed impedance grounding switch that is mechanically interlocked.
It is a further object of the present invention to provide an impedance grounding switch device that is timed to automatically close into a load bank impedance just before the feeder circuit breaker opens.
It is still a further object of the present invention to provide a vacuum circuit breaker with an integral high-speed impedance grounding switch that can be applied and operated in the range of 400 volts to 38 kilovolts.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.